This invention relates to metal-glass seals and more particularly to composite metallic articles which are capable of being sealed within glass materials in a vacuum-tight manner.
The invention further relates to methods of making composite metallic articles.
Perhaps the best known composite metal glass-sealing material on the market today is sold under the trade name "Dumet" and consists of a nickel-iron core sheathed in a copper sleeve or shell. The copper constitutes about 21 to 25 percent of the total weight of the material and is usually affixed about the nickel-iron core by swaging, welding, molten dipping, etc. One significant problem with "Dumet" has centered around the bond between the core and sleeve portions. The substantial difference in the coefficients of thermal expansion between the respective portions of the "Dumet" has on occassion contributed to interface separations, cracks, and similar voids particularly when the article was subjected to the elevated temperatures and compression pressures typical of some glass sealing operations.
A second problem inherent in a cylindrically-shaped composite article which consists of two metallic materials having widely different thermal expansions concerns the relatively large differentials between radial and longitudinal (axial) thermal expansions when the article is subjected to the aforementioned glass sealing processes. "Dumet" normally averages approximately 2.degree. variations under such conditions when measured with a commonly known testing device, the polariscope. Such variations in expansion can adversely affect a proper "match" between glass and composite article, resulting in cracks or similar voids in the glass portion of the product.
Still another problem of using "Dumet" as a glass-sealing article is one of cost, particularly when considering the relatively high prices of copper and copper products.
It is believed therefore that a glass-sealing composite metallic article which overcomes the above disadvantages of "Dumet" and similar composite articles would constitute an advancement in the art.
It is further believed that a method for making said article would represent an art advancement.